Hydraulic system



Jan. 27, 1942. F, FREUNDEL ETAL 2,270,943

HYDRAULIC SYSTEM Filed June 27, 1940 2 Sheets-SheetI l A 2 Jnventont 75222, ezzn'eZ Jan. 27, 1942. F. FREUNDEL x-:T AL

HYDRA ULIG SYSTEM Filed June 27, 1940 2 Sheets-Sheet 2 Jn venforrr 79H22 Freu/7562.'

v vPatented Jan. 27, 1942 UNITED 'STATE and Heinrich Altolelltlml Dellll.' assigner: to kJunkers Finnen-mul- Germany, Motorenwerke Aktiengesellschaft, Dessau, Germany, a corporation of Germany l Application June 21, 1940, sei-u1 No.l 34u12 In Germany March 7.1939 y 11 claims. (ci. csc-97)' 'This invention relates to improvements in hydraulic systems, and refers to such systems. equipped with volume distributors, wherein means are provided for insuring that a plurality of pistons, each mounted in a cylinder, are moved, substantially uniformly and simultaneously, completely to the ends of their strokes.

In most hydraulic systems of this general nature, due to structural inaccuracies or for other reasons, it often happens that the pistons do not move together and some, or one, of them never completes its stroke and reaches its end position. This even occurs when volume distributors are employed due to the fact that they may not distribute the ilow with sumcient accuracy. The main disadvantage of not moving the pistons simultaneously and uniformly when a volume distributor is used is that, in conventional lay-- outs including a parallel flow to the cylinders,

, when the first piston reaches its end position and stops the entire flow to the cylinders ceases, and therefore the other piston, or pistons, cannot be moved to their predetermined end positions where, in many cases, piston locking means are provided to engage them. And even where automatic valves are employed for shutting off the flow to a cylinder in which the piston has reached its end position this same undesired result often occurs.

It is an object of this invention to provide hydraulic systems for use when volume distributors are used for dividing the flow substantially equally in a plurality of directions to actuate a plurality of pistons, or other movable parts, in-v cluding a releasing means for the liquid flowing in each direction so that after one piston has been moved to the end of its stroke itsreleasing means functions and permits a parallel ow to continue to all pistons so that the other pistons may still be moved to their predetermined end positions. For, as previously stated, with these volume distributors, as soon as the flow in any one direction therefrom stops the entire parallel flow through the distributor stops. Moreover these releasing means consist of relief valves which may be placed at different locations in the systems, even in the pistons themselves which are moved by the pressure flow if so desired. Y

This invention contemplates several detailedl` structural variations in all of which the same underlying principle occurs: Namely that a parallel flow through all the feed lines occurs, and is maintained even after the fastest moving piston has reached the end of its stroke so that the other pistons may also be brought to their' respective end positions; this, obviously, is necessary'when a volume distributor is employed for the reason already noted above.

Some of the modified structural embodiments herein contemplated include: An arrangement having a relief valve in each feed line from the distributor set to open at a pressure slightly in excess of normal working pressure to permit the flow from that feed line to pass through a free return to a reservoir after the piston moved .thereby has reached its predetermined end position, thus permitting a now to continue to the other and slower moving piston. or pistons. An arrangement including relief valves arranged betaweenv the feed lines so that when one piston reaches the end of its stroke the now from the feedline operating that piston then passes into the other feed line to augment the iiow therethrough. Another arrangement wherein a common relief valve is connected to two feed lines so that the flow through either line, after the piston actuatedthereby has reached its end position, passes through a free return and to a reservoir. Yet another arrangement includes electrical means operated by either piston as it reaches its end position and opens a relief valve l in the feed line to that piston to permit a ilow to continue through that line by by-passing it back to the reservoir.

The various embodiments above referred to are hereinafter more fully described with the aid of the-accompanying drawings, wherein:

v Figure 1 illustrates a diagrammatic view of a hydraulic system including separate relief valves in the feed lines each connected to a free return to a reservoir. l

Figure 2 shows dlagrammatically a modied system wherein the feed lines are connected to one another by relief valves.

Figure 3 is a further modication wherein a relief valve common to two feed lines is connected by a free return to a reservoir, and

Figure 4 shows another modification wherein relief valves in the feed lines are electrically operated.

Referring to the drawings, i and 2 are cylinders having pistons 3 and l therein from which operating rods 5 and 6 respectively project, and which are primarily intended to operate mechanism such as landing gears on airplanes. Connected to thereservoir 1 by a suction line 1a is a pump tions a, b and c through any one of which the flow may be discharged as desired. 'I'he connections a and c (the latter terminating. in a pipe Il) are connected to volume distributors I8 and 3I respectively of known construction, which may be of the type illustrated and described in the patent to Klein 2,242,002, May 13, 1941. The distributor I8 divides the flow equally into the feed lines I2, I4 and I3, I5; and the distributor 3| equally divides the flow through the feed lines I8 and I9. The feed lines I4, I9, I5 and I8 are connected to the extremities I" and I', and 2" and 2 of the cylinders I and 2 respectively. The control valve connection b terminates in a free return line I6 to the reservoir I,- and the discharge side of the pump 8 is also connected to the return line I6 through a safety valve 32 which limits the pressure maintained in the system.

As the volume distributors I8 and 3I cannot always be relied upon to distribute the ow through the feed lines I4, I9, I5 and I8 with sumcient accuracy to insure both pistons reaching their predetermined end positions in their cylinders I and at exactly the same time relief valves are provided to permit continued flow through the volume distributor and the feed lines fed through it after the first piston has reached its position at one extremity or the other of its cylinder.

In the arrangement shown in Figure 1, ltwo relief valves 2| and 22 are employed which are connected to the feed lines I2, I4 and I3, I5 respectiv'ely. These relief valves are each also connected to the free return line I6 and are set to open at a pressure slightly in excess of the normal operating pressure in the system so that when either `piston 3 or 4 reaches the outer extremity (I or 2') of its travel an excess pressure is built up in the feed line, I4 or I5, through which the flow occurred to move that piston. This excess pressure opens the relief valve, 2I or 22, connected to that feed line so that a flow continues through that valve and the return line I8 back to the reservoir I, as well as through the other feed line to continue to move the piston which has not yet reached its end position. Thus a parallel flow continues for without it passage from the volume distributor to the piston which has not finished its stroke could not occur.

lSimilarly when the pistons 3 and 4 are being moved to the cylinder extremities I" and 2" the flow passes through the volume distributor 3I and the feed lines I9 and I8 which have other relief valves 23 and 24 respectively connected thereto and are also suitably" connected to the` return line I8. 'I'hus by manipulation of the control valve 3 the flow may be directed to either` volume distributor I8 or 3I (or directly to the return line I6 when the valve is neutrally positioned) to move the pistons 3 and 4 to either extremity of their strokes with the assurance that both pistons will reach their outer or inner cylinder extremities even if one piston does so somewhat in advance of the other. rlhe numeral 28 denotes cases, or rectifying device containers, to house the separate sets of relief valves 2I and 22, and 23 and 24;

In the modification shown in Figure 2, the arrangementdiifers in that opposed relief valves 25 and 28 connecting they feed lines I2, I4 and I3, I5 are provided so that when further ow through one feed line is prevented because the piston actuated thereby has reached the end of its stroke flow from that feed line then passes through one of the relief valves into the other `the circuit so that feed line thus permitting continued movement of the other piston by combined flow through both feed lines I2, I4 and I3, I5 thereinto from the volume distributor I8. Movement of the pistons in the reverse direction occurs similarly through the feed lines ,I8 and I8 which are similarly connected to one another by opposed relief valves housed within the c ase 28.

In the modification shown in Figure 3 the pipes or feed lines I2 and I3 are connected to opposite ends of a cylinder 2'I having a floating plunger 21a therein. Centrally of its length this cylinder 2'I is connected to a relief valve 28 which is also suitably connected to the return line I8. Consequently excess pressure built up in either feed line I2, 'I4 or I3, I54 causes movement of the plunger 21a so that the flow from that line may pass through the relief valve, after having moved the plunger 21a, and through the return line I8 to the reservoir I. Within the case 28 a similar combination of a cylinder, as shown at 21, having a plunger therein, and a relief valve, as shown at 28, are also provided which are suitably connected to the feed lines I9 and I8 through which a flow occurs past the volume distributor 3I when the pistons 3 and 4 are being moved inwardly.

In the modification shown in Figure'4 relief valves 29 and 38 are provided in the feed lines I2, I4 and I3, I5 respectively through which a flow occurs to move the pistons 3 and 4 to the extremities I' and 2 respectively of their cylinders. Both these relief valves 29 and 38 are again connected over the line I'I and three-way control valve 9 to the return line I8, but in this instance these valves are electrically operated and controlled by solenoids 33 and 34 respectively which are energized by circuits closed by movement of the pistons 3 and 4.

Mounted adjacent the cylinders I and 2 are longitudinally slidable members 41 and 48 having inwardly projecting extremities adapted to be engaged by trips 39 and 48 extending from the rods 5 and 6 respectively. Connected to the members 4'I and 48 are leads 52 and 53 respectively which extend to opposite sides of a source of power 54, and 4I indicates a switch in the lead 53. Extending from the members 4'I and 48 are contacts 41a and 48a which are electrically connected to the lines or leads 52 Spaced on opposite sides of each contact 41a and 48a are fixed contacts 35 and 35a, and 38 and 36a respectively. Extending from the contacts 35 and 35a are leads 5I and 58 which are connected also to the solenoids 33 and 34 respectively, and extending from the contacts 38 and 38a are other leads 58 and 55 which are also connected to the solenoids 33 and 34 respectively.

If the piston 4 is first moved toits outward position 2' by a flow entering the cylinder 2 from the feed line I 5 then the contact 48a is moved into engagement with the. contact 38a by movement of the lmember 48 which is shifted by the trip 48. Then a circuit is closed through the leads 53. 55, the solenoid 34, Aand theleads 58 and 52 through the contacts, 35a and 41a, because during the preceding movement of the piston 3 to the inner extremity, I", of its stroke the contacts 41a was moved into engagement with the contact 35a. However as that piston is moved to the outer end of its travel the member 4l is moved by the trip 39 and that contact 41a is brought into engagement with the contact 35 thereby breaking both relief valves are again closed. A similar solenoid operated arrangement and 53 respectively.

may also be provided for operating the relief valves housed in the case 20 and connected to the feed lines I9 and I8.

In Figure 1 yet another modified arrangement is shown also. The piston 4 is provided with opposed relief valves 31 and 38 extending therethrough, so that in the event the flow through the feed line l5 causes the piston 4 to reach the end 2' of its stroke before the piston 3 reaches its stroke extremity I' then that now may continue through the `valve 31 and escape through the pipe I8, the volume regulator 3| which is then not working, to the control valve 9 wherein the outlets b and c are then connected as the discharge from the pump 8 is being directed through the outlet a, and through the return line I6 to the reservoir I. Or again the valve 38 is opened when the flow entering from the feed line I8 has moved the piston 4 first to the opposite 'end of its stroke, so that this flow may continue through that relief valve 38 and return similarly through the feed line I5.

While in the foregoing the preferred embodiments of the invention have been described and shown, it is understood that still other alterations and modifications may be made thereto provided they fall within the scope of the appended claims.

What we claim is:

1. A hydraulic system in combination with moving aircraft parts comprising a pumping unit, a plurality of cylinders having pistons therein, a volume distributor connected to the discharge side of the pumping unit, a plurality of feed lines extending in parallel from the distributor to the cylinders for the pressure flow passing therethrough to actuate the pistons therein, and pressure releasing means connected to the feed lines whereby a parallel flow is continued through all the latter after the piston in one cylinder has reached its limit of travel.

2. In a hydraulic system, the combination set forth in claim 1, wherein the pressure releasing means consists of opposed relief valves connecting the feed lines whereby the ow from the feed line to one cylinder, after the piston therein has reached its limit of movement, augments the ow in the other feed line. 3. In a hydraulic system, the combination. set forth in claim 1, wherein the pressure releasing means consists of a relief valve connected to each feed line intermediately of its length.

4. In a hydraulic system, the combination set forth in claim l, wherein the pressure releasing means consists of a relief valve connected to each feed line, and electrical means for operating each relief valve including a `switch mechanism actuated by movement of each piston as it reaches the end of its stroke.

5.- In a hydraulic system, the combination set forth in claim 1, wherein the pressure releasing means consisting of a centrally apertured cylinder connected at each extremity to one of the feed lines, a plungervin the cylinder normally closing the aperture, and a relief valve connected to the cylinder aperture whereby either feed line may be connected to the relief valve by movement of the plunger.

6. In a hydraulic system, the combination of a reservoir, a pumping unit having its suction side connected thereto, a volume distributor connected to the discharge side of the pumping unit, a plurality of cylinders having pistons therein, va separate feed line from the distributor to each cylinder, a return line connected to the reservoir, and pressure releasing means connected to said feed lines and said return line whereby the now through any feed line is by-passed through the return line to the reservoir when the flow through that `feed line stops due to the piston actuated by that ow having reached its limit of travel in its cylinder. x

7. In a hydraulic system, the combination set forth in claim 6, including a pipe having a safety valve therein extending from the discharge line between the pump and the volume distributor to the return line to limit the pressure of liquid passing through the volume distributor, either pressure releasing means being adapted to be opened by excess pressure in its feed line caused by resistance offered by the piston in the cylinder connected to that feed line after said piston has completed its stroke.

8. A hydraulic system for use in combination with moving aircraft parts comprising a pumping unit, a plurality vof cylinders having pistons therein, a volume distributor connected to the discharge side of the pumping unit, a plurality of feed lines extending in parallel from the distributor to the cylinders, and pressure releasing means connected to the feed lines at points ref moved from the cylinders whereby a parallel flow is continued through said lines after a piston in one cylinder becomes stationary at any point throughout its limit of travel.

9. A hydraulic system for use in combination with pairs of aircraft parts adapted to move in unison throughout equal distances of travel comprising a pumping unit, a plurality of cylinders having pistons therein, a volume distributor connecter to the discharge side of the pumping unit,

'cylinder normally closing a plurality of feed lines extending in parallel from the distributor to the cylinders, and pressure releasing means connected to the feed lines, said pressure releasing means being set to operate at a pressure exceeding that normally required to operate the pistons and so arranged in each path of uid travel as to permit continued flow through the parallel feed lines when either piston meets undue resistance to travel in its cylinder.

10. The arrangement set forth in claim 9 wherein the pressure releasing means comprises opposed relief valves connecting the feed lines whereby the flow from the feed line to one cylinder augments the flow in the other feed line after the piston in said mst-mentioned cylinder has reached its limit of travel.

l1. 'I'he arrangement set forth in claim '9 wherein the pressure releasing means comprises a centrally apertured cylinder connected at each end to one of the feed lines, a plunger in the the aperture, and a relief valve' connected to the cylinder aperture whereby either feed line may be connected to the relief valve by movement of the plunger.

. FRITZ FREUNDEL.

HEINRICH ROSENTHAL. 

